Chlorine production



Feb. 20, 1951 A. J. JOHNSON ET AL CHLORINE' PRODUCTION Filed Nov. 8, 1948 inventors:

Ava J- Johnson Patented Feb. 20, 1951 CHLORINEI PRODUCTION Ava J. Johnson, Oakland, and Alexander J.

n Cherniavsky, San Francisco, Calif., assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application November 8, 1948, Serial No. 58,828

This invention relates to improvements in the execution of catalytic processes wherein chlorine is produced by the oxidation of hydrogen chloride. The invention relates more particularly to improvements" in the manufacture of chlorine bythe oxidation of hydrogen chloride in the presence of a halide of a metal of variable valence.

Hydrogen chloride is produced asa by-product in a great number of processes. Often, its production exceeds the need for this undesired product. Not only does the conversion of more valuable charge material to this undesired product detract materially from economical operation of the process on a practical scaleI but presents serious disposal problems. An ecnomfical source of chlorine, on the other hand, is generally in considerable demand. Often processes` .lproducing hydrogen chloride themselves employchlorine as a starting material. Methods enablingthe more economical production of chlorine from available hydrogen chloride are therefore of great value to the industry.

A method disclosed heretofore for the production of chlorine from hydrogen chloride comprises bringing the hydrogen chloride into contact with a halide of a metal of variable valence in the presence of an oxygen-containing gas at an elevated temperature thereby forming reaction products including chlorine and water. The method may be represented by Vthe overall formula:

Economical operation of such-a process is generally dependent to at least a substantial degree upon the efciency with which separation of individual components from the reactor eilluence can be accomplished. Difficulties, generally necessitating recourse to complex and costly operational procedures in process available heretofore, is occasioned by the fact that the reactor eluence comprises gaseous components, such as chlorine and hydrogen chloride, which must be separated from one another, as well as Water which forms an azeotrope with hydrogen chloride. The reactor eilluence will generally comprise a considerable amount of unconverted hydrogen chloride and economical operation of the process requires that it be returned to the reaction zone. Since water is also a product of the reaction its constant separation from such recycled hydrogen chloride must be resorted to. Removal of water from hydrogen chloride within the system is, however, essential not only to eliminate water formed during the reaction but `avoid the passage of inordinately large volumes of material through the reaction zone and other parts of the system. Hydrogen chloride which contains only a relatively small amount of water is generally considerably more corrosive than more dilute hydrogen: chloride. It is therefore essential to eilicient--,operation that substantially complete water removal be accomplished economically within the4 system. When resorting to the use of a fluidized/A catalyst system the ability to .eilect substantially complete removal of the water is often of particular importance since hydrogen chloride is employed as a means to effect 'the transportation of fluidized catalysts within portions of the equipment in which water is generally excluded. Since the hydrogen chloridewater azeotrope contains a considerable proportion of water and hydrogen chloride feed is generally available in the aqueous form, it is generally highly desirable to effect the removal of water from the hydrogen chloride feed prior to its passage to the reaction.

It is an object of the present invention to provide an improved .process enabling the more efcient production of chlorine by the oxidation of hydrogen chloride. l

In accordance with the invention, hydrogen chloride is contacted with oxygen in a reaction zone in the presence of'a chloride of a metal of variable valence under hydrogen chloride oxidizing conditions thereby forming reaction products comprising chlorine and water. Euence from the reaction zone comprising chlorine, hydrogen chloride and water, is contacted with a hydrogen chloride absorbing medium consisting of a cooled stream of aqueous hydrogen chloride in a hydrogen chloride absorbing zone, thereby absorbing substantialy all of the hydrogen chloride con-` tent of said reactor effluence in the aqueous hydrogen chloride stream. The gaseous portion of the reactor efluence remaining uncondensed and unabsorbed and consisting essentially of chlorine free from any substantial amount of hydrogen chloride is passed from the hydrogen chloride absorbing zone to a suitable chlorine dehydrating zone wherein water is removed therefrom by contact with a dehydrating agent. The aqueous hydrogen chloride absorbing medium enriched with the absorbed hydrogen chloride is passed from the hydrogen chloride absorbing zone to a hydrogen chloride stripping zone. Within the stripping zone a vapor overhead consisting essentially of anhydrous hydrogen chloride is separated from a liquid bottoms consisting essen-r Ltially of aqueous hydrogen chloride. A part of the liquid bottoms are passed from the stripping zone to the hydrogen chloride absorbing zone to be used as the absorbing medium therein. The remainder of the liquid bottoms` formed in the stripping zone are passed to an eXtractive distillation zone wherein they are subjicteditolextractivev distillationv in: the presence of an"K auxiliary-'S014 vent having a greater affinity for Water than for hydrogen chloride under extractive distillation? resulting in the formation of a vaporoverhead consisting essentially of anhydrous "hydrogen" chloride. The substantially..anhydrous chloride overhead from the extractiv di "illation z'orief In a preferred modication of the invention the? is passed to the reaction zone? Y auxiliary solvent employed iri. tl;1i e.extractivefdisstillation zone is first introduced into the chlorine type. Thus the invention may be applied to processes Whereirrthe oXidaiticnLjof. the .hydrogen chloridefislectdL withiv-the faid. of conventional hydrogen chloride oxidation catalysts employed .Tin-the form of solid beds or in the orrn of molten fluids.- .Though but one reactor is shown in the drawing, 'it is to be understood that two or more 1 '.izeactors; connected. in series or parallel flow, may .suitablybef employed. Such reactors may comprise' cnven onal reaction Zones of the type dis- `"tlf/sed assutablefor the execution of the hydro- 1 gen-chlorideioxidation, including those wherein dehydrating zone to function as the chlorine'd'e'- hydrating agent thereinbbefore being passed to thefextractive dist' 1ationl1zone-mf f Inlor'der ftoset'ff more .tully-.theLna-turerf theiinventiorrit Willi e describedlin. detail .herein with reierence. to lthelattachededrawing wherein the# single' ligure:V represents: aimcre orlless diag grammatical elevationalviewof; one forrnzof. ap, paratus suitable .fori executing. theprocess. of. the invention.. .v f

. I 'leydrouslhydrogenrchloride, or an anhydrous ogen chloride-containing fugas, .is passed tlftrou'ghline.7 'I finto::afireactiongzone .The .reactiorrfzoneimayicompiseza chamber Ltype: of. re.- actor I.2.1. C1Xygen=;is dntroducedi into the system Vby?.means` oa-line .1.31. leadinginto .line, AI El; passing intofreactor I 2 ..Thexoxygenthusintroduced into thefsy'stemmay;consist' essentially-of oxygen, lor

contamina-a chloride of .coppenasgthaative eredient. Infradditign- @ofthe .-rn,eta1 Chloridesl 0f :the rgt. transition series. the coniametfialis ,tivatins assets, .web es fer. essere@ e fhlrlldfe cadmiurm. tin, .antimony,lth alkali and alkaj ridefemplcyed 'may beu'sfed assueh o y suitable supprtor'diluent materials' example, adsorpt'ivematerials f sili us and/or 'aluminum characterand' o fsynthetcor nataral l`origin. Particularlypreferred"supportrdihrent 'mat-erialsJY comprise "alumina, vk"silica,"'imajgnsia silicataluminacarbon; ull'ersiearthtand the like.

3 1l? a' preferred method 1f-"executingthe-'invern v "tion the-contactmass'comprising themetall chlol'rid'esg iseriiploydinthe fiuidi-zed'state; Particullari'yflfreferredfluidizedcontact"rrrasses"comprise aiifinelyjdividedialuminousimaterialimpregnated -withcopperhhloride Thecontact;mass-ismain- 4tained. in the1Tl1n'dizedor suspended v-stateiwithin the reaction Zonesby. theigaseousreaetants themselves. @ptionallyiadditiona nertzgasamay.: erin- .troducedintonthesystenr bymeansfnol' S thc-.drawina f onsistfof;.anooxygemcontainingV gas, such .filtretemperature*within reactor I2A isi-rnain-V taine nthe rangefof f .from about Y300 .Cr tov aboutrdf C: and.. preferably. lfrom` about 1001"A C., toialooutil-(lo C. -Sucatmospheric; atmospheric-or supera-tmospheric: pressuresnma-y' y'be maintained Within reactor I2. .The 11.rse.of.f.a slightlysuperatmosphericpressu're.rangingiffor example, from about 5 to-about fipounds .gauge.is generally preferred. The rategofhydrogen chloride. introductionY into the- ;reaction-zone is controlled to maintain .a stoichiometrical "excess of i .hydrogen chloride over the oxygen passedinto vthe reaction zone., .'fhusfgthefmolal ratio of hydrogen chloride to oxygen` may lb e. maintained in the` ratio of :from about 11.5.1159 about 15, and-preierably from alwutltozabouth'-f Y -f. lfeatingmeans such Vas; for example,v an -indirect heat exchanger I5, and optionally -other heating means-.suc has.a. iurnacawnot shownin the drawingrareprovided. for providing the -initial-.heatrequired starting up theoperation.

Under-.fthe `alcove-zdeineol conditions hydrogen vchloride is. oxidized fin reactor I 2 rwith thelforrna- 2tion. of Ireactionproducts consisting essentially of chlorineand water. f .Reaction products areelimf i from the :reaction chamberJZ til'llQlll'l of excess-heat'.frorrrireactorfl2.v Removaltot exportion oflthe catalyst from-reactor I2. toV cata- II 4,; dischargingfinto passed through line l24, provided with cooler 25, into a hydrogen chloride absorbing zone. In passing through cooler the stream is cooled tol a temperature suiciently low to condense rsubstantially all the water content of the stream.

The hydrogen chloride absorbing zone may comprise a scrubber 26.

Within scrubber 28 the stream comprising reaction products is brought into countercurrent contact with la cooled liquid absorbing medium, such as an aqueous solution of hydrogen chloride obtained within the system and introduced into the upper part of column 26 by meansof line 21. The reaction products will comprise a ratio of hydrogen chloride to water of reaction substantially in excess of that comprised in the waterhydrogen chloride azeotrope; for not only is hydrogen chloride and water produced in substantially equimolar amounts in the hydrogen chloride oxidation reaction but a substantial excess of hydrogen chloride is generally charged to the reaction zone. Within column 26 substantially all of the hydrogen chloride introduced by means of line 24 Will be absorbed by the aqueous hydrogen. chloride introduced through line 21, leaving a gaseous overhead consisting essentially of chlorine free of any substantial amount of hydrogen chloride. The gaseous overhead from column 26 consisting essentially of chlorine; a minor amount of water, and any inert gases introduced into, or formed Within, the system, is passed through line 29-to a suitable chlorine dehydrating zone. The amountof water contained in the overhead from column 25 will generally not exceed about 2-3% by weight. The greater part of the water entering column 26 leaving with the enriched absorbing medium. The chlorine dehydrating zone may comprise a suitable column 39 wherein the chlorine stream is .brought into direct contact with a suitable dehydrating agent introduced into the column by means of line 3|. may be employed. Suitable chlorine dehydrating agents comprise,v sulfuric acid, a concentrated solution of a hygroscopic salt, such as calcium chloride, or the like. Substantially anhydrous gaseous overhead. consisting essentially of chlorine, is taken overhead from column 30 by means of lineA 34. The chlorine thus removed from column 30 through line 34 is passed to storage and optionally to suitable means for the removal4 of any inert gas therefrom, such'as, for example, a low temperature distillation not shown in the drawing.

The dehydrating agent is introduced into the upper part of column 30 from an outside source by means of valved lines 32 and 3|. Dehydrating agent comprising the Water removed from the chlorine stream is removed from column 30 by means of line 33 and eliminated from the system by means of valved line 35. 4

Liquid bottoms consisting essentially of aqueous hydrogen chloride enriched with the absorbed hydrogen chloride is passed from column 21 through line 40 into a hydrogen chloride stripping zone. .A .part of the liquid passing through line is by-passed through line 4|, `provided With cooler 42, and returned to the column 26 to remove heat of absorption.

lThe hydrogen chloride stripping zone may comprise a stripping column 44. Within column 44 the enriched aqueous hydrogen chloride stream is subjected to stripping conditions forming a gaseous overhead consisting essentially of anhydrous hydrogen chloride and liquid bot- Any suitable type of dehydrating agent.

toms consisting essentially of the hydrogen chloride-water azeotrope. chloride bottoms will generally contain about 21% by Weight of hydrogen chloride.

The substantiallyanhydrous hydrogen chloride is taken overhead from column 44 and passed through line 45 provided with cooler 46 into an accumulator 41. From accumulator 41 the substantially anhydrous hydrogen chloride is passed through lines 48 and |0 to reactor l2. A part of the hydrogen chloride is by-passed from line 48 through valved line 49 to column 44 as reiiux. l

Liquid bottoms consisting essentially of aqueous hydrogen chloride containing hydrogen chloride vand Water in the proportion of the azeotrope are taken from column 44 through valved line 5|. A part of the aqueous hydrogen chloride stream is passed from line 5| through line 21 provided with cooler 52 to the upper part of column 26 to be used as the hydrogen chloride absorbing medium employed therein. In passing through cooler 52 the stream is cooled to a temperature suiiiciently low to assure absorption of all hydrogen chloride in column 26 and condensation of any water vapor present therein. When char-ging aqueous hydrogen chloride to the system at least a part of such aqueous hydrogen chloride charge may be introduced into line 21 by means of valved line 28.

The remainder of the aqueous hydrogen chloride` stream flowing through line 5| which is not passed to column 26 is passed to suitable water removing means. The water removing means i may comprise anextractive distillation column 55. Within column 55 the aqueous hydrogen chloride stream is subjected to extractive distillation in the presence of anfauxiliary solvent having a greater preference for water than hydrogen chloride. Preferred auxiliary solvents comprise the concentration aqueous solutions of a hygroscopic salt which has a vapor pressure not greater,

than about 8 mm. of-mercury at about 20 C. Examples of such suitable hygroscopic salts are calcium chloride, calcium bromide, zinc chloride, magnesium chloride, calcium iodide, ferrie chloride, and the like. Of the suitable hygro'scopic salts calcium chloride is preferred. The aqueous salt solutions should preferably have a concentration of from about 10% to about 60% by weight depending upon the solubility of the particular salt employed. Calcium chloride solutio'nshaving a concentration in' excess of30% by weight, and preferably about 55% by weight, are preferably employed.

The concentrated aqueous solution of the hygroscopic salt, such as, for example, a concentrated aqueous calcium chloride solution is introduced into the upper part of extraotive distillation column 55'by means of valved line 55. Within column 55 theiaqueous hydrogen chloride is-extractively distilled with the formation of a substantially anhydrous hydrogen chloride overhead and liquid bottoms consisting essentially of aqueous calcium chloridev comprising substantially all of the water introduced into column`55 with the aqueous hydrogen chloride stream. The substantiallyanhydrous hydrogen chloride overhead is passed from extrae-tive distillation co1- umn 55 through line |0 to the reactor |2.

Aqueous calcium chloride is taken from the bottom of column 55 and passed through line 51 through suitable neutralizing means, such as a drum containing calcium carbonate 58 and t thence through line 58 Ainto an auxiliary solvent The aqueous hydrogen tractive distillation of the aqueous hydrogen chloride.

It is seen that the process of the invention not only enables the eicient separation of the gaseous reaction products but provides for the eicient removal of the water content not only from the reactor eiiiuence but from aqueous hydrogen chloride feed to the system in the complete absence of any substantial loss of hydrogen chloride. The process of the invention therefore, enables operation in the absence of the passage of any substantial amount of water to the reaction zone and yet enables substantially complete conversion of all of the hydrogen chloride charged to the system to desired substantially anhydrous chlorine product with a minimum of operative steps.

For the sake of clarity in setting forth the nal Y ture of the invention, parts of apparatus such as,

for example, pumps, compressors, valves, fractionators, condensers, catalyst storing means, accumulators, stills, and the like, not essential to a full and complete understanding of the invention have been omitted from the drawing.

We claim as our invention:

1. In a process wherein chlorine is produced by contacting oxygen and hydrogen chloride with a chloride of a metal having an atomic number of from 21 to 30, both inclusive, at hydrogen chloride oxidizing conditions in a reaction zone,

thereby forming a reaction mixture consisting essentially of chlorine, hydrogen chloride and Water, the steps which comprise cooling said reaction mixture to a temperature sufficiently low to condense substantially all of the Water content of said mixture, thereafter contacting the cooled reaction mixture in an absorption zone with a cooled liquid absorbing medium consisting essentially of an azeotropic mixture of hydrogen chloride and water, thereby absorbing in said absorbing medium substantially all of the hydrogen chloride contained in said reaction mixture with the formation in said absorption zone of an enriched aqueous hydrogen chloride absorbing medium containing hydrogen chloride in excess of that of the hydrogen chloride-water azeotrope and leaving a residual gas phase consisting essentially of chlorine substantially free of hydrogen chloride but containing a small amount of water, stripping excess hydrogen chloride in anhydrous form from said enriched absorbing medium in a stripping zone, thereby leaving aqueous hydrogen chloride as liquid stripper bottoms, extractively distilling anhydrous hydrogen chloride vapor from at least a portion of said liquid stripper bottoms in an extractive distillation zone in the presence of an auxiliary solvent having a greater preference for water than hydrogen chloride emanating from within the system as described below, dehydrating said chlorine-containing gas phase formed in said ab* sorption Zone by contact with a dehydrating agent consisting essentially of a concentrated aqueous solution of a hygroscopic salt containing from. about 10% to about 60% by weight of said hygroscopic salt and having a vapor pressure not greater than about 8 mm. Hg at about 20 C. in a chlorine dehydrating zone, thereby forming in said chlorine dehydrating zone a liquid phase consisting essentially of said dehydrating agent and absorbed Water and leaving a gas phase consisting essentially of anhydrous chlorine, passing said liquid phase from said chlorine dehydrating Zone to said extractive distillation zone to be used therein as said auxiliary solvent emanating from within the system, and passing anhydrous hydrogen chloride from said stripping and extractive distillation zones to said reaction zone.

2. The process in accordance with claim l wherein said dehydrating agent is a concentrated aqueous solution of calcium chloride.

3. The process in accordance with claim 1 wherein said metal having an atomic number of from 21 to 30 is copper.

AVA J. JOHNSON. ALEXANDER J. CHERNIAVSKY.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 118,212 Deacon Aug. 22, 1871 2,204,172 Balcar A June 11, 1940 2,299,427 Rosenstein Oct. 20, 1942 2,357,095 Evans et al Aug. 29, 1944 2,436,870 Murphree Mar. 2, 1948 

1. IN A PROCESS WHEREIN CHLORINE IS PRODUCED BY CONTACTING OXYGEN AND HYDROGEN CHLORIDE WITH A CHLORIDE OF A METAL HAVING AN ATOMIC NUMBER OF FROM 21 TO 30, BOTH INCLUSIVE, AT HYDROGEN CHLORIDE OXIDIZING CONDITIONS IN A REACTION ZONE, THEREBY FORMING A REACTION MIXTURE CONSISTING ESSENTIALLY OF CHLORINE, HYDROGEN CHLORIDE AND WATER, THE STEPS WHICH COMPRISE COOLING SAID REACTION MIXTURE TO A TEMPERATURE SUFFICIENTLY LOW TO CONDENSE SUBSTANTIALLY ALL OF THE WATER CONTENT OF SAID MIXTURE, THEREAFTER CONTACTING THE COOLED REACTION MIXTURE IN AN ABSORPTION ZONE WITH A COOLED LIQUID OBSORBING MEDIUM CONSISTING ESSENTIALLY OF AN AZEOTROPIC MIXTURE OF HYDROGEN CHLORIDE AND WATER, THEREBY ABSORBING IN SAID ABSORBING MEDIUM SUBSTANTIALLY ALL OF THE HYDROGEN CHLORIDE CONTAINED IN SAID REACTION MIXTURE WITH THE FORMATION IN SAID ABSORPTION ZONE OF AN ENRICHED AQUEOUS HYDROGEN CHLORIDE ABSORBING MEDIUM CONTAINING HYDROGEN CHLORIDE IN EXCESS OF THAT OF TH EHYDROGEN CHLORIDE-WATER AZEOTROPE AND LEAVING A RESIDUAL GAS PHASE CONSISTING ESSENTIALLY OF CHLORINE SUBSTANTIALLY FREE OF HYDROGEN CHLORIDE BUT CONTAINING A SMALL AMOUNT OF WATER, STRIPPING EXCESS HYDROGEN CHLORIDE IN ANHYDROUS FORM FROM SAID ENRICHED ABSORBING MEDIUM IN A STRIPPING ZONE, THEREBY LEAVING AQUEOUS HYDROGEN CHLORIDE AS LIQUID 